For Tcl_ListObjAppendList, this points to a list value
containing elements to be appended onto listPtr.
Each element of *elemListPtr will
become a new element of listPtr.
If *elemListPtr is not NULL and
does not already point to a list value,
an attempt will be made to convert it to one.

For Tcl_ListObjAppendElement,
points to the Tcl value that will be appended to listPtr.
For Tcl_SetListObj,
this points to the Tcl value that will be converted to a list value
containing the objc elements of the array referenced by objv.

int *objcPtr (in)

Points to location where Tcl_ListObjGetElements
stores the number of element values in listPtr.

An array of pointers to values.
Tcl_NewListObj will insert these values into a new list value
and Tcl_ListObjReplace will insert them into an existing listPtr.
Each value will become a separate list element.

int *intPtr (out)

Points to location where Tcl_ListObjLength
stores the length of the list.

int index (in)

Index of the list element that Tcl_ListObjIndex
is to return.
The first element has index 0.

Tcl list values have an internal representation that supports
the efficient indexing and appending.
The procedures described in this man page are used to
create, modify, index, and append to Tcl list values from C code.

Tcl_ListObjAppendList and Tcl_ListObjAppendElement
both add one or more values
to the end of the list value referenced by listPtr.
Tcl_ListObjAppendList appends each element of the list value
referenced by elemListPtr while
Tcl_ListObjAppendElement appends the single value
referenced by objPtr.
Both procedures will convert the value referenced by listPtr
to a list value if necessary.
If an error occurs during conversion,
both procedures return TCL_ERROR and leave an error message
in the interpreter's result value if interp is not NULL.
Similarly, if elemListPtr does not already refer to a list value,
Tcl_ListObjAppendList will attempt to convert it to one
and if an error occurs during conversion,
will return TCL_ERROR
and leave an error message in the interpreter's result value
if interp is not NULL.
Both procedures invalidate any old string representation of listPtr
and, if it was converted to a list value,
free any old internal representation.
Similarly, Tcl_ListObjAppendList frees any old internal representation
of elemListPtr if it converts it to a list value.
After appending each element in elemListPtr,
Tcl_ListObjAppendList increments the element's reference count
since listPtr now also refers to it.
For the same reason, Tcl_ListObjAppendElement
increments objPtr's reference count.
If no error occurs,
the two procedures return TCL_OK after appending the values.

Tcl_NewListObj and Tcl_SetListObj
create a new value or modify an existing value to hold
the objc elements of the array referenced by objv
where each element is a pointer to a Tcl value.
If objc is less than or equal to zero,
they return an empty value.
The new value's string representation is left invalid.
The two procedures increment the reference counts
of the elements in objc since the list value now refers to them.
The new list value returned by Tcl_NewListObj
has reference count zero.

Tcl_ListObjGetElements returns a count and a pointer to an array of
the elements in a list value. It returns the count by storing it in the
address objcPtr. Similarly, it returns the array pointer by storing
it in the address objvPtr.
The memory pointed to is managed by Tcl and should not be freed or written
to by the caller. If the list is empty, 0 is stored at objcPtr
and NULL at objvPtr.
If listPtr is not already a list value, Tcl_ListObjGetElements
will attempt to convert it to one; if the conversion fails, it returns
TCL_ERROR and leaves an error message in the interpreter's result
value if interp is not NULL.
Otherwise it returns TCL_OK after storing the count and array pointer.

Tcl_ListObjLength returns the number of elements in the list value
referenced by listPtr.
It returns this count by storing an integer in the address intPtr.
If the value is not already a list value,
Tcl_ListObjLength will attempt to convert it to one;
if the conversion fails, it returns TCL_ERROR
and leaves an error message in the interpreter's result value
if interp is not NULL.
Otherwise it returns TCL_OK after storing the list's length.

The procedure Tcl_ListObjIndex returns a pointer to the value
at element index in the list referenced by listPtr.
It returns this value by storing a pointer to it
in the address objPtrPtr.
If listPtr does not already refer to a list value,
Tcl_ListObjIndex will attempt to convert it to one;
if the conversion fails, it returns TCL_ERROR
and leaves an error message in the interpreter's result value
if interp is not NULL.
If the index is out of range,
that is, index is negative or
greater than or equal to the number of elements in the list,
Tcl_ListObjIndex stores a NULL in objPtrPtr
and returns TCL_OK.
Otherwise it returns TCL_OK after storing the element's
value pointer.
The reference count for the list element is not incremented;
the caller must do that if it needs to retain a pointer to the element.

Tcl_ListObjReplace replaces zero or more elements
of the list referenced by listPtr
with the objc values in the array referenced by objv.
If listPtr does not point to a list value,
Tcl_ListObjReplace will attempt to convert it to one;
if the conversion fails, it returns TCL_ERROR
and leaves an error message in the interpreter's result value
if interp is not NULL.
Otherwise, it returns TCL_OK after replacing the values.
If objv is NULL, no new elements are added.
If the argument first is zero or negative,
it refers to the first element.
If first is greater than or equal to the
number of elements in the list, then no elements are deleted;
the new elements are appended to the list.
count gives the number of elements to replace.
If count is zero or negative then no elements are deleted;
the new elements are simply inserted before the one
designated by first.
Tcl_ListObjReplace invalidates listPtr's
old string representation.
The reference counts of any elements inserted from objv
are incremented since the resulting list now refers to them.
Similarly, the reference counts for any replaced values are decremented.

Because Tcl_ListObjReplace combines
both element insertion and deletion,
it can be used to implement a number of list operations.
For example, the following code inserts the objc values
referenced by the array of value pointers objv
just before the element index of the list referenced by listPtr:

result = Tcl_ListObjReplace(interp, listPtr, index, 0,
objc, objv);

Similarly, the following code appends the objc values
referenced by the array objv
to the end of the list listPtr: